Sending data over voice channels has been known at least since the development of the modem. Schemes such as sub-band signaling, cellular digital packet data, and the like are examples of using a voice channel to communicate data.
In the past, however, the voice channel was a reasonably linear one, defined by bandwidth and response. In most modern wireless devices, a vocoder is used to reduce the voice to a low bandwidth digital signal. Although the vocoder algorithms are specifically designed to minimize the perceptible distortion of voice signals, the audio path provided is nonlinear and time varying, and not suitable for typical data signals. This is a particular concern when mission critical information requires sending, as users are often relegated to manual repetition of the data verbally. If the user is distracted, incapacitated, or simply unable to reach his radio when communication is needed, severe harm may result.
While the same physical channel may be available for sending non-voice data, access to this path is often not provided outside of the device itself. Accessories needing data communications access are not always granted access to this path. Even access to basic signaling functions, such as an emergency switch, are often denied to third party accessories.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.